This invention relates to compositions containing cholesteric liquid crystalline phase materials and their utilization. More particularly, the invention relates to a composition of a cholesteric liquid crystalline phase material and oil-soluble dyes, and to a venapuncture method employing the composition for vein location.
Cholesteric liquid crystalline phase materials, also referred to as cholesteric liquid crystals, their technology and applications are reviewed in the book by Peter L. Carroll entitled "Cholesteric Liquid Crystals", June, 1973 (Ovum Ltd., London). The materials, hereinafter referred to for convenience simply as "liquid crystals", are a class of compounds that display a cholesteric mesophase within certain temperature limits. When liquid crystals are in such phase, and ordinary white light is directed at the material, the light is separated essentially into two components, one of which is transmitted and one of which is scattered or reflected. The scattered light gives the material an irridescent color, which depends upon the material, the temperature, and the angle of the incident light beam. The cholesteric mesophase is a state of matter intermediate in molecular ordering between a crystalline solid and an isotropic liquid. In general, the materials are colorless in their solid and isotropic liquid states, assuming the coloration of their background or of light-absorptive materials added thereto.
Prior patents relating to thermal color responsive or temperature sensitive cholesteric liquid crystal compositions and their use in applications where temperature is to be measured or a temperature pattern is to be observed include U.S. Pat. Nos. 3,114,836, 3,441,513 and 3,533,399, the latter patent having to do with the production of visible patterns corresponding to skin temperature patterns in human beings. Reports on the application of liquid crystal thermography to examination of the body include an article by Davison, Ewing, Fergason, Chapman, Can, and Voorhis, "Detection of Breast Cancer by Liquid Crystal Thermography", Cancer, Vo. 29, No. 5, page 1123, May, 1972, and an article by Davison, Ewing, Sayat, Mulla, and Fergason, "Liquid Crystal Thermographic Placental Location", Obstetrics and Gynecology, Vol. 42, No. 4, page 574, October, 1973.
In order to improve color contrast, the liquid crystals commonly are applied to and viewed against an absorptive, particularly a black background, which serves to absorb the transmitted light. Alternatively, absorptive, generally black particulate material is admixed with the liquid crystals, so as to absorb the transmitted light while not interfering excessively with the intensity of the scattered light. As an additional alternative, it has been proposed to incorporate black or colored dyes in the liquid crystal compositions. The incorporation of dyes is disclosed in the above-identified book by Carroll, particularly, pages 102 and 197, the patents identified therein, i.e., U.S. Pat. Nos. 3,647,279 and 3,666,947 and West German Pat. No. 2,012,493, and also U.S. Pat. Nos. 3,627,699 and 3,656,909.
Liquid crystal compositions in which black pigments or oil-soluble black dyes are incorporated provide the black background needed for observing liquid crystal coloration. However, color intensity is diminished with their use, so that they are added in proportions such as to balance the desired colored contrast with the color intensity. As a result, neither contrast nor intensity reaches a desired level for certain applications. While colored dyes have been incorporated in liquid crystal compositions, as disclosed in the patents and publication identified above, it appears that they have been used principally to accomplish other objectives, such as to absorb ultraviolet or infrared radiation.
The most common technique for applying liquid crystals to measure or map temperatures, as on a surface of the body, is to first blacken the surface with an aqueous, oil-impervious black paint, then apply liquid crystals from a solution by brushing or spraying. This procedure is time-consuming, and cannot be used when instant observation of temperatures or thermal gradients is required. Liquid crystals dispersed in films and having a black backing or black filler for absorbing transmitted light have been applied to surfaces, including body skin, for measuring temperatures and for thermal mapping. The use of films for rapid temperature measurement and thermal mapping has been limited owing to their inability to conform to surface contours.
There has long been a need for a rapid method of greater reliability for locating veins in the human body, in hospitals, clinics and laboratories, preparatory to drawing blood or making intravenous injections or infusions. While body vascular patterns have been mapped by liquid crystal thermography, as reported in the references identified above, the prior techniques have not been applied to the problem of effecting venapuncture in the human body, apparently due to the limitations thereof which prevent such an operation from being effected rapidly and/or reliably.